Many deaf individuals are not exposed to language during the first four years of life. Deficits in morphological and syntactic processing are associated with delayed exposure to language, but there are currently no studies of perceptual processing in this population. The long-term goal of the research program is to investigate the effects of delayed exposure to language during the critical period on the development of perceptual processing skills later in life. The current grant project investigates the specific hypothesis that individuals who are not exposed to a language in early childhood will not be able to ignore meaningless phonological variability during perceptual processing. Three studies explore this hypothesis by comparing the sign perception skills of native signers, deaf individuals who acquired American Sign Language (ASL) after the age of 9 and hearing individuals who acquired ASL as a second language after the age of 9. Study 1 modifies the Gating Task for use with digitized signed stimuli to explore how much phonological information subjects need to identify signs in ASL. Study 2 modifies the Phoneme Monitoring Task for use with digitized signed stimuli to compare the ability of subjects to extract phonemes from different phonological contexts. Study 3 uses synthetic signs in a Phoneme Identification and Discrimination Task to investigate whether individuals in the three subject groups categorize the visual signal into the same phonological categories, with particular attention to the location of category boundaries.